What exactly do you mean by "follows lines really badly"? If you mean darts from side to side while turning hard and going over bumps, then you probably have bump steer. If you mean that the car pulls to the left or the right while going straight on uneven roads (straight ridges, grooves, etc.), then I don't think this is related to bump steer.

Wider, lower-profile tires with stiff sidewalls will tend to follow road grooves more dramatically than narrow, high-profile tires with soft sidewalls. A square-shouldered tire may tend to exaggerate this effect . Also changes in alignment could aggravate this (ie. positive camber could dig the outer edge of the tire into road irregularities sooner than a negative camber adjustment). The same thing that makes these tires responsive and provide feedback also makes them annoying on poor roads.

I immediately noticed an increase in this effect when changing from 16x8 wheels with 245/16 tires to 7x9.5 wheels with 275/17 tires. Your SS of course came with the 17" wheels. To some degree, it is a compromise that you have to make for better response and performance. As an extreme example, an F1 racecar, is very twitchy and requires constant corrections on rougher roads.

 

"What exactly do you mean by "follows lines really badly"? If you mean darts from side to side while turning hard and going over bumps, then you probably have bump steer. If you mean that the car pulls to the left or the right while going straight on uneven roads (straight ridges, grooves, etc.), then I don't think this is related to bump steer."

Right. If the wheels are not moving substantially up and down, this is not bumpsteer.

"Also changes in alignment could aggravate this (ie. positive camber could dig the outer edge of the tire into road irregularities sooner than a negative camber adjustment). "

This works the other way around. Positive camber stabilizes the car, which is why the factory setting is positive camber. Negative camber generates more cornering force, but it's less stable. Note that the inside edge can also "dig into road iregularities".

 

SStupid

Did you get your alignment checked (and reset) after installing the springs? Particularly your static toe and equality of right vs left camber. Even a little toe-out will feel twitchy in many normal driving situations.

The lower ride height will make your suspension operate over a different part of the bumpsteer curve, probably resulting in greater rates of toe change for a given amount of bump than at OE ride height.

Norm

 

Regarding positive vs negative camber; they are both going to contribute to "nibbling" on uneven ridges. However, since the outer edge of the tire is further away from the pivot point of the steering, positive camber theoretically is going to have greater leverage on changing the direction of the car on uneven roads. Therefore, on a square-shouldered aggressive tire, positive camber could contribute to nibbling more.

I have an old beater Toyota P/U which is lowered 2" and I can't get a 0 camber adjustment on it. It nibbles alot for a little 225/16 tire with a positive offset wheel. Oh, negative offset wheels really aggravate "nibbling".

Of course, SStupid is on the right track regading looking at hub bearing, tie-rod or bushing looseness. I don't know how many miles he has on the car. Excessive deflection in these areas could also lead to a wandering effect when those big tires nibble on uneven roads.

I replaced my ABS/bearing hubs with new units for $90 from Pep Boys 5 months ago just to make damn sure that my new 13.15"-rotor brake calipers had maximum clearance from the wheels.

 

SS....your problem probably isn't due to bumpsteer. Problems with excessive bumpsteer are usually encountered when the suspension is changing attitude. If your car catches ruts and cracks etc.....it can be due to wide tires, additional negative camber than stock and worn tie rod ends or VERY work wheel bearings. You'd notice the wheel bearing though...it would have to be pretty darn loose to cause your problem. I replace my front hub/bearings every two summers or so since I do alot of track events and some races. The higher heat levels of the brakes and continuous cornering forces. I'd just check the tie rod ends,the sockets in the rack, and the ball joints. Wide tires(275) and a decent amount of camber will cause the car to floow ruts in the road etc.......no getting around it most of the time.

 

I did get my car aligned after my initial installation of the pro-kit. I had no trouble at the time, but the car did settle another 1/2 inch or so from initial installation.

Oh yeah, I have 75K on the car. I think somebody asked about that.

I have a road here in Austin that is often traveled and is very bumpy. My car will jerk in different directions after hitting one of these bumps without the steering wheel even moving. I also notice the car will take its own path suddenly on the highway as if it found a rail to follow. That is the best I can describe the sensation I am feeling. Next week, I will get the alignment checked again and probably replace the tie rod end with factory replacements to see if there is still a problem. I will let you guys know. I can't tell you how much I appreciate all of your help.

I was looking at my camber while standing in front of the car today. It is noticably negative, even to the naked eye.